Wildfires have roared through canyons, hillsides and residential areas in densely populated Southern California for a fourth day, while gusting winds hampered firefighters' efforts to knock down the flames.

Authorities fear the four major fires — ranging from Los Angeles up the Pacific coast to Santa Barbara County — could be whipped up by the region's notorious westward Santa Ana winds that could reach hurricane strength.

The winds, which blow in hot and dry from the California desert, could reach 120 kilometres per hour and create "extreme fire danger," according to an alert sent by the countywide emergency system in Los Angeles.

The National Weather Service said high winds were expected to continue until Saturday.

The fires, which broke out on Monday and Tuesday, have reached into the wealthy enclave of Bel-Air on Los Angeles' West Side. Some major highways in the densely populated area were intermittently closed.

No civilian casualties or fatalities have been reported but three firefighters were injured, the Los Angeles Fire Department said.

"I was expecting this year to see snow on that mountain and now the thing is on fire."

Because of the heavy smoke, the South Coast Air Quality Management District warned residents, especially the elderly, children, pregnant women and people with respiratory diseases, to stay inside.

The Thomas Fire, the largest in the area, continued its westward push on Thursday, forcing a few hundred Santa Barbara County residents to be evacuated and the closing of coastal Highway 101 north of Ventura city.

The fire has destroyed more than 150 homes and threatened thousands more in Ventura.

Additional evacuations were called for in the Ventura area, where 50,000 people had already fled their homes over the last three days.

About 100 firefighters fended off flames in the seaside enclave of Faria Beach, caught between burning mountains and the Pacific Ocean, northwest of Ventura.

Fires spread down the smoking hills, jumping the heavily used US 101 highway, and headed toward clusters of beach houses. Firefighters lined up along a railroad track, the last barrier from the flames.

The fires are the second outbreak to ravage parts of California this autumn.

The celebrated wine country in the northern part of the state was hit by wind-driven wildfires in October that killed at least 43 people, forced some 10,000 to flee their homes and consumed at least 9,900 hectares north of the San Francisco Bay area.

The California Department of Insurance said the northern California blazes caused insured losses of more than US$9 billion ($12 billion).